The present invention relates to a method and apparatus for forming a clip of die-formed fasteners, hereinafter referred to as nails, ready for insertion into an impact-fired pneumatic or manual nailer or equivalent, and the resulting fastener clip product.
A known method of forming clips or assemblies of nails for pneumatic or manual nailers is as follows. Nails are stamped out of approximately 2.2-inch wide by 0.061-inch thick C1008 steel which is provided in 800 to 900-pound coils. This size coil provides sufficient material for about 200,000 nails. Other coil dimensions and other materials may be used. The nails are formed in a 30-ton press or equivalent using 10 progression dies or equivalent. The nails are formed head to toe. For instance, the head of the first nail is on the right-hand edge of the strip, while the head of the second nail is on the left-hand edge. Although the strip is nominally 0.061-inches thick, it can still be within thickness specification if it is slightly wedge-shaped, with the thickness of the right-hand edge differing from that of the left-hand edge by as much as 0.0005-inches. The nail is approximately symmetric in two ways about its longitudinal axis. This axis is a line of symmetry or the center line of the material. Facing this center line from the side of the nail, the nail appears substantially rectangular with 0.0305-inches of material, nominally on either side of the center line. Facing the center line from the broad face of the nail, the nail has a press-formed head above a tapering body. The body of the nail is trapezoidal with the side of the trapezoid remote from the head almost forming a point. There is a region of serration over a portion of the nail to enhance the fastening function. The serration is directionally shaped to impede the extraction of a nail after being driven. The nails are approximately 2-inches long with approximately a 0.25-inch head.
After forming, the first nail moves down through a bolster and enters a carrier on the right, the second nail moves through a corresponding bolster and enters a carrier on the left. The motion is not smooth. The nails move in 0.061-inch increments, driven by the pressure of the press at more than 500 increments per minute. The objective of the operation is to form and ship a clip having approximately 100 nails ready for insertion into an impact-fired pneumatic or manual nailer. To form the clip, adhesive is applied by wiping along both sides of the nails as they are moved in the 0.061-inch increments. Ideally, the clip is continuous. However, the currently used method is far from ideal. The vibration, tolerances and the variable properties of the adhesive combine to cause quality control problems. Due to vibration, sometimes a clip will break, leaving a smaller clips containing fewer nails. The viscosity of the adhesive varies with atmospheric conditions causing the amount of adhesive material applied to vary unacceptably. If excessive adhesive is applied, clips sometimes stick together in the shipping carton. Worse, a clip with excessive adhesive can jam the user""s nailer. If insufficient adhesive is used, clips will break into pieces resulting in scrap. In the presently used method, the manufacturing operators are required to visually inspect work-in-process. If the adhesive is too heavy, the operator reports the condition to the upstream facility and an adjustment is made. The clip is not guaranteed to be robustly formed. To meet specification, the bow (curve) in the clip must be less than about 0.015-inches. The packing operators are required to gage the clips for bow and to square them before packing. This is labor intensive and, therefore, expensive. If the operator judges that a clip is not sufficiently square, the operator places that clip in an air-driven press to square it. Due to tolerances, right and left-hand nails are sufficiently different in the process that they must be kept segregated through the formation of clips. In addition, the curing adhesive results in toxic fumes requiring ventilation. The adhesive used is flammable and presents a fire hazard. Due to these problems, the known method currently in use is unsatisfactory in both yield and expense. Moreover, the method creates environmental hazards and safety problems for the production workers.
The present invention is a method and an apparatus for forming a clip of nails for use in an impact-fired pneumatic or manual nailer. As in the known method, nails are stamped out of steel strip, preferably out of approximately 2.2-inch wide by 0.061-inch thick C1008 steel provided in 800 to 900-pound coils, which is sufficient material for about 200,000 nails. Other dimensions and other materials may be used. The nails are formed in a 30-ton press or equivalent using ten progression dies or equivalent. The finished nails are formed head to toe. The head of the first nail is on the right-hand edge of the strip. The head of the second is on the left-hand edge. The strip is nominally 0.061-inches thick, but can still be within specification tolerance if it is slightly wedge-shaped, with the right-hand edge differing from the left-hand edge by no more than 0.0005-inches.
Four precision fixtures are mounted on a rotatable turret. Each fixture has a coordinate reference system. Nails exit the press on the right-hand and left-hand bolsters. Loose nails in groups of 100 are alternately fed into one of the fixtures. Each fixture is adapted to precisely square the loose nails so that the heads of the nails are substantially planar and that the longitudinal center lines of the nails are substantially in a single plane. The fixture holds 100xc2x12 nails, since the exact number of nails which the fixture will hold is a function of the material thickness and process tolerances. Any number in this range is satisfactory for use in a pneumatic or manual nailer. When the first fixture is full, that is the nails placed therein will form an appropriate length clip satisfying a minimum number of nails, the turret rotates 90xc2x0. Such rotation places a new fixture in proper position to receive and align the next approximately 100 nails in the aforementioned two planes. Upon this 90xc2x0 rotation, the first, full, fixture is now positioned at the welding system. The nails in the fixture are maintained in position. An optical servomechanism locates the position where the first nail and the second nail in the fixture abut with respect to the reference location. This positional information is captured in computer storage, and the servomechanism proceeds to locate the position where the second and third nails abut. The servomechanism continues to operate in this fashion until all the nail abutment points are recorded. After it is mechanically possible, a computer-operated laser-based welding head follows the optical servomechanism. The laser-based welding system, which is keyed to the same reference point, retrieves the stored coordinate data from the computer storage. The welding head is moved translationally from the reference point to the coordinate of the first and second nail abutment, whereupon the first and second nails are spot welded to form a partial clip. The two spot welds assure that the first two nails maintain the planarity of the top surface of the nails and the planarity nails"" center lines that was previously established when the nails were positioned in the precision fixture. The welding system retrieves the next coordinate and the welding-head is translated to the next coordinate where the third nail is spot welded to the partial clip. The process continues until the clip is complete. In a 100-nail clip, 198 spot welds are performed, resulting in the fixing of the nails into a 100-nail clip. The actual number of welds can vary due to the aforementioned allowable xc2x12 variation in nail count per clip. This operation requires significantly less time than the nail formation and loading and precision alignment at the press position. The turret rotates 90xc2x0, resulting in the first clip being positioned at the unloading station. The second set of approximately 100 nails is positioned for welding. A third set of nails is precisely aligned in a third fixture. The operation is continuous. No adhesives are used. Each clip is precisely formed and there is no requirement for special handling of out-of-square clips in packing.
It is the primary object of the present invention to provide a clip of approximately 100 nails for a pneumatic or manual nailer that is adhesive-free, therefore presenting no possibility for jamming the feed in the nailer due to adhesive fragments or excessive bowing.
Another object of the present invention is to provide a clip of approximately 100 nails for a pneumatic or manual nailer with sufficiently uniform bond strength between adjacent nails that the clips remain bonded and mechanically stable throughout subsequent handling, shipping and insertion into a nailer.
Another object of the present invention is to provide a clip of approximately 100 nails for a pneumatic or manual nailer with sufficiently uniform bond strength between adjacent nails that to hold the clip securely in a nailer so substantially no problems arise when driving the nails with the nailer.
Another object of the invention is to provide a method for manufacturing clips of nails for a pneumatic or manual nailer with substantially no environmental effluents, and no highly flammable materials, resulting in substantially improved worker safety, and without requiring the use of protective breathing apparatus.
An additional object of the invention is to provide a method for manufacturing clips of nails for a pneumatic or manual nailer with a substantially improved manufacturing yield by reducing scrap to virtually zero when compared with the known methods.
An additional object of the invention is to provide a method for manufacturing clips of nails for a pneumatic or manual nailer with substantially improved manufacturing throughput.